09-18-2015, 10:33 PM
This all arises from the after market naturally following the path of least resistance to getting into Grendels.
Since every company other than Colt ignored the requirements of the 7.62x39 rim thickness, and thought that .124" face depth would be fine, that is what a lot of companies started going with. The 7.62x39 AR world is filled with broken extractors as a result. Even the .308 after-market suffers from extractor problems, and those are substantially wider than an AR15 extractor.
The terms "Type I" and "Type II" originated with BHW as best as I can tell having followed this over the years, as VASCAR describes.
No matter what face depth you go with, you need a tool steel exctractor that is produced by a shop that knows their heat treating well, and has very tight QC on parts. That applies to any cartridge/caliber in the AR15 and self-loading weapons in general. Extractors take a beating, especially with shorter gas systems.
Les Baer uses .136" bolts. 264 LBC-AR refers more to a chamber design, not a bolt face depth.
Since every company other than Colt ignored the requirements of the 7.62x39 rim thickness, and thought that .124" face depth would be fine, that is what a lot of companies started going with. The 7.62x39 AR world is filled with broken extractors as a result. Even the .308 after-market suffers from extractor problems, and those are substantially wider than an AR15 extractor.
The terms "Type I" and "Type II" originated with BHW as best as I can tell having followed this over the years, as VASCAR describes.
No matter what face depth you go with, you need a tool steel exctractor that is produced by a shop that knows their heat treating well, and has very tight QC on parts. That applies to any cartridge/caliber in the AR15 and self-loading weapons in general. Extractors take a beating, especially with shorter gas systems.
Les Baer uses .136" bolts. 264 LBC-AR refers more to a chamber design, not a bolt face depth.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
www.AR15buildbox.com